A. Manigandan

Bio: A. Manigandan is an academic researcher from Anna University. The author has contributed to research in topics: Magnetization & Orthorhombic crystal system. The author has an hindex of 3, co-authored 8 publications receiving 44 citations. Previous affiliations of A. Manigandan include University College of Engineering.

Effect of Divalent Cation Substitution in the Magnetoplumbite Structured Bafe12o19 System

Abstract: Synthesis of magnetically ordered barium hexaferrite powders and the adjustment of magnetic properties for perpendicular magnetic recording media are realized through substitution of divalent cation (Ca) in the BaFe12O19 system. The Ca2+ substituted Ba1−xCaxFe12O19 (where x = 0.05, 0.1, 0.15 and 0.2) compounds have been prepared through solid state reaction technique. The powder X-ray diffraction analysis reveals that all the prepared compounds crystallized in magnetoplumbite hexagonal structure and the flat hexagonal platelet morphology of the crystallites was identified through scanning electron microscopy. The formation of magnetoplumbite structured Ba1−xCaxFe12O19 system due to mechanical activation was supported by micro-Raman measurements. Both pure and Ca substituted BaFe12O19 compounds exhibit sharp intense peaks which reveals defect free environment in the crystal lattice. From the room temperature magnetization studies, it was observed that the saturation magnetization (MS) and remanent magnetization (MR) values drastically decreases for the Ba0.95Ca0.05Fe12O19 compound which may be due to the existence of spin canting effect and leads to the reduction of super exchange fields. The increase in MS and MR values for the Ba0.9Ca0.1Fe12O19 and Ba0.85Ca0.15Fe12O19 compounds could be attributed to the enhanced hyperfine fields at 12k and 2b sites due to the strengthening of Fe3+–O–Fe3+ super exchange interactions. A large reduction in the coercivity value from 3,090 to 1,548 Gauss may be attributed to the fall in magneto crystalline anisotropy. The high temperature magnetization studies infer that while increasing substitution level of Ca in the BaFe12O19 system results in decreasing trend in Curie temperature. The room temperature dielectric measurement shows that the incorporation of Ca2+ in the BaFe12O19 system results with increase in the dielectric constant and this case substantiates the space charge polarization. The magnetically ordered BaFe particulate having higher saturation and low coercivity values with superior magnetic and dielectric behaviour exhibiting the possibility for future high-recording-density storage products.

Structural, Magnetic and Dielectric Studies on Strontium Substituted Nd2CuO4 System

Abstract: The substitution of Strontium on T'–structured Nd2CuO4 system has been carried out through solid state reaction tech-nique. From the Powder XRD patterns, it is found that the compounds are formed in single phase and crystallizes in orthorhombic structure. The variation in lattice parameters with decreasing nature of volume of the prepared com-pounds confirms the incorporation of lower atomic radii Strontium in Neodymium site. Surface morphology and ele-mental composition studies are also carried out to know the nature of the compounds and effect of Strontium substitu-tion in Nd2CuO4 system. The paramagnetic nature of all the prepared compounds has been identified through magnetization studies and the results are correlated with the electron spin resonance studies by the way of variation in resonance field and broad peak width. Increasing order of dielectric constant on higher doping concentration of Strontium and the least value of dielectric loss at higher frequencies confirms the improved surface transport properties of the prepared compounds.

Inducing multiferroic behaviour in the diamagnetic Y2O3 system

Abstract: The synthesis and characterization of Y2−xFexO3 (where x = 0–0.3) compounds has been carried out for their importance in the field of multiferroic materials. The powder X-ray diffraction reveal that the compounds Y1.95Fe0.05O3, Y1.9Fe0.1O3, Y1.85Fe0.15O3 and Y1.8Fe0.2O3 crystallize in tetragonal structure whereas Y1.75Fe0.25O3 and Y1.7Fe0.3O3 compounds crystallize in orthorhombic structure. The change in crystal system with respect to the concentration of Fe may be attributed to the variation in occupancy position of Fe3+ into the Y3+ site of Y2O3 system. Variation in crystal structure, surface morphology and composition was studied by micro-Raman analysis, SEM and EDX analysis. The shift in intense Raman signals from 426 to 385 cm−1 confirms the change in the crystal structure of the prepared compounds. Further it is also identified that the Eg mode of vibration is the dominant in the Fe substituted compounds. The substitution of Fe in the Y2O3 system leads to the increase in the intensity of resonance band, which indicates a large polarisability variation in the Y2−xFexO3 compounds. Diffused reflectance studies show a red shift in energy gap values while increasing the concentration of Fe. The room temperature magnetization and electron paramagnetic resonance studies reveal that the incorporation of Fe in the Y2O3 system leads to magnetic phase change from diamagnetic to ferromagnetic. The electric polarization studies imply that the substitution of lower ionic radii element Fe3+ in the Y3+ site leads to distortion in the lattice and show the way to spontaneous dipole moment and it was found that the Y1.8Fe0.2O3 compound exhibits the possibility of multiferroic behaviour. Therefore this paper explores the possibility of inducing ferromagnetic and ferroelectric behaviour in the Fe substituted yttrium oxide system.

Structural and magnetic property studies on BaREBiO4 (where RE = Sm and Nd) system

Abstract: The new ceramic compounds type BaREBiO4 (where RE = Sm and Nd) have been reported for the first time. The sample was prepared by solid-state reaction technique. The orthorhombic crystallization with a = 6.429(4) A, b = 6.536(5) A, c = 8.648(4) A for BaSmBiO4 and a = 6.485(3) A, b = 6.561(4) A, c = 8.686(4) A for BaNdBiO4 was studied from powder X-ray diffraction studies. The semiconducting nature of the compounds was observed with the energy gap measurement from diffused reflectance spectroscopy (DRS) studies. The paramagnetic nature of the compounds at room temperature and low temperature conditions was identified by magnetization measurements as a function of magnetic fields and temperature. The effective magnetic moment of the samples was found to be 2.126 μB and 4.272 μB.

Effect of calcination temperature on microstructure, dielectric, magnetic and optical properties of Ba0.7La0.3Fe11.7Co0.3O19 hexaferrites

Abstract: M-type barium hexaferrite Ba 0.7 La 0.3 Fe 11.7 Co 0.3 O 19 (BaLCM) powder, synthesized using sol gel auto combustion method, heat treated at 700, 900, 1100 and 1200 °C. X ray diffraction (XRD) powder patterns of heat treated samples show the formation of pure phase of M-type hexaferrite after 700 °C. Thermo gravimetric analysis (TGA) reveals that the weight loss of BaLCM becomes constant after 680 °C. The presence of two prominent peaks, at 432 cm −1 and 586 cm −1 in Fourier Transform Infrared Spectroscopy (FT-IR) spectra, gives the idea of formation of M-type hexaferrites. The M – H curve obtained from Vibrating Sample Magnetometer (VSM) were used to calculate saturation magnetization ( M S ), retentivity ( M r ), squareness ration (SR) and coercivity (H c ). The maximum value of coercivity (5602 Oe) is found at 900 °C. The band gap dependency on temperature was studied using UV–vis NIR spectroscopy. The dielectric constant has been found to be high at low frequency but it decreases with increase in frequency. Such kind of dielectric behavior is explained on the basis of Koop׳s phenomenological theory and Maxwell Wagner theory.

Effect on dielectric, magnetic, optical and structural properties of Nd–Co substituted barium hexaferrite nanoparticles

Abstract: M-type barium hexaferrite [Ba1−x Nd x Co x Fe12−x O19 (x = 0.0–0.5) (BNCM)] powders, synthesized using citrate precursor method, were heat treated at 900 °C for 5 h. The pattern of powders, when subjected to X-ray diffraction, shows the formation of M-type hexaferrite phase. The formation of BNCM, from thermogravimetric analysis/differential thermal analysis/derivative thermogravimetry, is observed to be at 440 °C. The presence of two prominent peaks near 430 and 580 cm−1 in Fourier transform infrared spectroscopy spectra indicates the formation of M-type hexaferrites. The M–H curves obtained from vibrating sample magnetometer were used to calculate saturation magnetization (M S), retentivity (M R), squareness ration and coercivity (H C). UV–Vis NIR spectroscopy reveals that band gap depends on size of the crystallites. The dielectric constant is found to be high at low frequency and decreases with increase in frequency. This kind of behaviour is explained on the basis of Koop’s phenomenological theory and Maxwell–Wagner theory.

Remarkable Magnetic Exchange Coupling via Constructing Bi‐Magnetic Interface for Broadband Lower‐Frequency Microwave Absorption

Abstract: Severe lower‐frequency (2–8 GHz) microwave pollution caused by the rapid development of 5th generation (5G) communication posts significance on cutting‐edge microwave absorbers. However, the intensely coupled wave‐impedance and microwave dissipating ability dramatically hinder their performance in the exact lower‐frequency range. The rationally designed heterostructure of hard/soft ferrite composite provides an efficient solution to address the issue. In this context, core‐shell structured hard/soft BaFe(12‐x)CoxO19@Fe3O4 with abundant heterointerface is created using facile spray‐drying and subsequent solvothermal approach, where hard magnetic BaFe(12‐x)CoxO19 serves as the core and soft magnetic Fe3O4 serves as the shell, respectively. The unique core‐shell integration contributes sufficient magnetic exchange coupling interaction for strong magnetic loss beyond Snoek's limitation, which considerably boosts a lower‐frequency microwave absorption. Accordingly, the minimum reflection loss (RLmin) of typical BaFe11.6Co0.4O19@Fe3O4 microcomposite reaches −48.9 dB at the thickness of 3.5 mm, its bandwidth of reflection loss < −10 dB can cover almost all the S and C bands (2.6–8 GHz). Generally, an easy and controllable pathway is conveyed in this work to encourage improved magnetic loss ability as well as decouple the wave‐impedance and microwave dissipating ability in magnetic composites, which widens the road to the development of advanced lower‐frequency magnetic absorbers.